Spend time learning the maps you play on trust me it helps a lot, such as grenade placements, weapon spawns, jumps etc anything to help you slay on that particular map.
Also learn to be good with all weapons because no doubt you will go into a match an not get your intended weapon and you may be stuck with a weapon you don't want, but practice in customs with friends, and while your at it learn teamwork with them as well ;D
Just a few tips.